Diabetes mellitus is a serious disease afflicting over 100 million people worldwide. In the United States, there are more than 12 million diabetics, with 600,000 new cases diagnosed each year. Diabetes mellitus is a diagnostic term for a group of disorders characterized by abnormal glucose homeostasis resulting in elevated blood sugar. There are many types of diabetes, but the two most common are Type 1 (also referred to as insulin-dependent diabetes mellitus or IDDM) and Type 2 (also referred to as non-insulin-dependent diabetes mellitus or NIDDM).
The etiology of the different types of diabetes is not the same; however, everyone with diabetes has two things in common: overproduction of glucose by the liver and little or no ability to move glucose out of the blood into the cells where it becomes the body's primary fuel.
People who do not have diabetes rely on insulin, a hormone made in the pancreas, to move glucose from the blood into the cells of the body. However, people who have diabetes either do not produce insulin or cannot efficiently use the insulin they produce; therefore, they cannot move glucose into their cells. Glucose accumulates in the blood creating a condition called hyperglycemia, and over time, can cause serious health problems.
Diabetes is a syndrome with interrelated metabolic, vascular, and neuropathic components. The metabolic syndrome, generally characterized by hyperglycemia, comprises alterations in carbohydrate, fat and protein metabolism caused by absent or markedly reduced insulin secretion and/or ineffective insulin action. The vascular syndrome consists of abnormalities in the blood vessels leading to cardiovascular, retinal and renal complications. Abnormalities in the peripheral and autonomic nervous systems are also part of the diabetic syndrome.
Diabetes has also been implicated in the development of kidney disease, eye diseases and nervous-system problems. Kidney disease, also called nephropathy, occurs when the kidney's “filter mechanism” is damaged and protein leaks into urine in excessive amounts and eventually the kidney fails. Diabetes is also a leading cause of damage to the retina at the back of the eye and increases risk of cataracts and glaucoma. Finally, diabetes is associated with nerve damage, especially in the legs and feet, which interferes with the ability to sense pain and contributes to serious infections. Taken together, diabetes complications are one of the nation's leading causes of death.
Many people with NIDDM have sedentary lifestyles and are obese; they weigh approximately 20% more than the recommended weight for their height and build. Furthermore, obesity is characterized by hyperinsulinemia and insulin resistance, a feature shared with NIDDM, hypertension and atherosclerosis.
Obesity, which is the result of an imbalance between caloric intake and energy expenditure, is highly correlated with insulin resistance and diabetes in experimental animals and human. However, the molecular mechanisms that are involved in obesity-diabetes syndromes are not clear. During early development of obesity, increased insulin secretion balances insulin resistance and protects patients from hyperglycemia (Le Stunff et al., Diabetes, 43:696-702 (1989)). However, over time, β-cell function deteriorates and non-insulin-dependent diabetes develops in about 20% of the obese population (Pederson, P., Diab. Metab. Rev., 5:505-509 (1989)) and (Brancati, F. L. et al., Arch. Intern. Med., 159:957-963 (1999)). Given its high prevalence in modern societies, obesity has thus become the leading risk factor for NIDDM (Hill, J. O. et al., Science, 280:1371-1374 (1998)). However, the factors which predispose a fraction of patients to alteration of insulin secretion in response to fat accumulation remain unknown. The most common diseases with obesity are cardiovascular disease (particularly hypertension), diabetes (obesity aggravates the development of diabetes), gall bladder disease (particularly cancer) and diseases of reproduction. Research has shown that even a modest reduction in body weight can correspond to a significant reduction in the risk of developing coronary heart disease.
Obesity considerably increases the risk of developing cardiovascular diseases as well. Coronary insufficiency, atheromatous disease, and cardiac insufficiency are at the forefront of the cardiovascular complication induced by obesity. It is estimated that if the entire population had an ideal weight, the risk of coronary insufficiency would decrease by 25% and the risk of cardiac insufficiency and of cerebral vascular accidents by 35%. The incidence of coronary diseases is doubled in subjects less than 50 years of age who are 30% overweight. The diabetes patient faces a 30% reduced lifespan. After age 45, people with diabetes are about three times more likely than people without diabetes to have significant heart disease and up to five times more likely to have a stroke. These findings emphasize the inter-relations between risks factors for NIDDM, obesity and coronary heart disease as well as the potential value of an integrated approach involving the treatment of both obesity and diabetes (Perry, I. J. et al., BMJ, 310:560-564 (1995)).
Type 2 diabetes results from the progressive loss of pancreatic β-cell function in the presence of insulin resistance, leading to an overall reduction in insulin output (Prentki, M. et al., “Islet failure in type 2 diabetes”, J. Clin. Invest., 116:1802-1812 (2006)). β-cells are the cell type that store and release insulin in response to an elevation in plasma glucose or in response to hormonal signals from the gut following the ingestion of food. Evidence suggests that in type 2 diabetics the rate of β-cell cell death (apoptosis) exceeds that of new β-cell development, yielding an overall loss in β-cell number (Butler, A. E. et al., “β-cell deficit and increased β-cellapoptosis in humans with type 2 diabetes”, Diabetes, 52:102-110 (2003)). β-cell apoptosis may arise from persistent elevations in plasma glucose levels (glucotoxicity) and/or plasma lipid levels (lipotoxicity).
G-protein coupled receptors (GPCRs) expressed on β-cells are known to modulate the release of insulin in response to changes in plasma glucose levels (Ahren, B., “Autonomic regulation of islet hormone secretion—Implications for health and disease”, Diabetologia, 43:393-410 (2003)). Those GPCRs specifically coupled to the elevation of cAMP via the Gs alpha subunit of G-protein, have been shown to enhance glucose-stimulated insulin release from β-cells. Cyclic AMP-stimulating GPCRs on β-cells include the GLP-1, GIP, β2-adrenergic receptors and GPR119. Increasing cAMP concentration in β-cells is known to lead to the activation of PKA which is thought to prevent the opening of potassium channels on the surface of the β-cell. The reduction in K+ efflux depolarizes the β-cell leading to an influx of Ca++ which promotes the release of insulin.
GPR119 (e.g., human GPR119, GENBANK® Accession No. AAP72125 and alleles thereof; e.g., mouse GPR119, GENBANK® Accession No. AY288423 and alleles thereof) is a GPCR located at chromosome position Xp26.1 (Fredricksson, R. et al., “Seven evolutionarily conserved human rhodopsin G protein-coupled receptors lacking close relatives”, FEBS Lett., 554:381-388 (2003)). The receptor is coupled to Gs, and when stimulated, produces an elevation in cAMP in a variety of cell types including β-cell-derived insulinomas (Soga, T. et al., “Lysophosphatidylcholine enhances glucose-dependent insulin secretion via an orphan G-protein-coupled receptor”, Biochem. Biophys. Res. Comm., 326:744-751 (2005), international patent applications WO 04/065380, WO 04/076413, WO 05/007647, WO 05/007658, WO 05/121121, WO 06/083491 and EP 1338651). The receptor has been shown to be localized to the β-cells of the pancreas in a number of species as well as in specific cell types of the gastrointestinal tract. Activation of GPR119, with agonist ligands such as lysophosphatidylcholine, produce a glucose dependent increase in insulin secretion from primary mouse islets and various insulinoma cell lines such as NIT-1 and HIT-T15 (Soga, T. et al., “Lysophosphatidylcholine enhances glucose-dependent insulin secretion via an orphan G-protein-coupled receptor”, Biochem. Biophys. Res. Comm., 326:744-751 (2005); Chu, Z. L. et al., “A role for β-cell-expressed GPR119 in glycemic control by enhancing glucose-dependent insulin release”, Endocrinology, doi:10.1210/en.2006-1608 (2007)).
When activators of GPR119 are administered to either normal mice or mice that are prone to diabetes due to genetic mutation, prior to an oral glucose tolerance test, improvements in glucose tolerance are observed. A short-lived increase in plasma glucagon-like peptide-1 and plasma insulin levels are also observed in these treated animals (Chu, Z. L. et al., “A role for β-cell-expressed GPR119 in glycemic control by enhancing glucose-dependent insulin release”, Endocrinology, doi:10.1210/en.2006-1608 (2007)). In addition to effects on plasma glucose levels, GPR119 activators have also been demonstrated to produce reductions in acute food intake and to reduce body weight in rats following chronic administration (Overton, H. A. et al., “Deorphanization of a G protein-coupled receptor for oleoylethanolamide and its use in the discovery of small-molecule hypophagic agents”, Cell Metabolism, 3:167-175 (2006), and international patent applications WO 05/007647 and WO 05/007658).